Logical Channel Prioritization in LTE MAC
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Solution Overview
Problem
Current LTE systems face inefficiencies in uplink channel prioritization and rate control, particularly in minimizing padding and handling control traffic and signaling radio bearers, which can lead to delays and resource underutilization.
Innovation Solution
The method involves prioritizing logical channels based on decreasing priority order, allowing negative MBR credits, and ensuring maximum use of available resources without limiting bucket size, while prioritizing control traffic over data and optimizing token/credit bucket updates to prevent padding and maximize resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If logical channels are served in strict priority order up to configured PBR and MBR, then priority handling between logical channels is improved, but resource utilization deteriorates due to padding and underutilization
Solution Approach 1:
The patent implements dynamic logical channel prioritization by allowing the prioritization parameters (PBR, MBR, priority levels) to be configured and updated dynamically through RRC signaling. The MAC entity adapts the serving order and resource allocation based on current channel conditions and QoS requirements, transitioning from static to dynamic priority handling to improve both reliability and resource utilization
Solution Approach 2:
The patent changes the parameters of logical channel prioritization by introducing configurable PBR (Prioritized Bit Rate), MBR (Maximum Bit Rate), and priority levels for each logical channel. These parameters can be adjusted through RRC configuration to optimize the balance between priority handling and resource utilization, allowing the system to adapt to different traffic patterns and QoS requirements
2Ease of operation
If uplink resources are limited by configured PBR and MBR, then rate control is improved, but transmission efficiency deteriorates due to padding
Solution Approach 1:
The patent applies partial rate control by allowing logical channels to exceed their configured MBR when necessary, rather than strictly limiting them. The MAC entity can allocate resources beyond MBR to avoid padding, achieving a balance between maintaining rate control for QoS compliance and improving transmission efficiency by utilizing available uplink resources fully
Solution Approach 2:
The patent makes rate control dynamic by allowing the MAC entity to adjust resource allocation in real-time based on available uplink resources, buffer status, and QoS requirements. The rate control parameters (PBR, MBR) are configured dynamically through RRC signaling, enabling the system to adapt to changing conditions and optimize transmission efficiency while maintaining adequate rate control
3Reliability
If MAC SDUs are prioritized and selected from different logical channels, then logical channel prioritization is improved, but complexity increases due to multiple prioritization rules
Solution Approach 1:
The patent segments the prioritization procedure into distinct steps: first serving logical channels in priority order up to PBR, then continuing with remaining resources up to MBR, and finally handling any leftover resources. This segmented approach maintains reliable prioritization while making the complex procedure more manageable and implementable through structured MAC layer logic
Data Source
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AI summary
A method and apparatus are disclosed for prioritizing logical channels when a new transmission is performed. Logical channel resources are allocated for available data to a plurality of logical channels. A maximum bit rate (MBR) credit (i.e., token) is decremented in a buffer (i.e., bucket) associated with a particular one of the logical channels by the size of a medium access control (MAC) service data unit (SDU). The MBR credit may have a negative value. If any of the allocated channel resources remain, the logical channels are served n a decreasing priority order until the data is exhausted. A radio link control (RLC) SDU is not segmented if the whole RLC SDU fits into the remaining resources. The MAC SDU excludes a MAC PDU header and MAC padding.